The present invention is directed to cryogenic, elastomeric closures for cryogen containers. More particularly, the invention is directed to elastomeric stoppers for vials, plungers for syringes, and other closures for containers of materials, which must be processed or stored at cryogenic temperatures.
Stoppers and similar closures for vials and other containers for biological and pharmaceutical samples are typically made of elastomeric materials which provide a number of important functional properties, which are desirable for the closures. These include high resistance to permeation or migration of the material inside the container to the outside (escape of the contained material), as well as high resistance to permeation or migration of gases and liquids into the container from the outside (container/sample contamination), excellent sealing properties between the closure and the opening of the container to be closed, easy insertability or application of the closure to the container opening, and easy puncturability of the closure by a syringe needle or other instrument to insert or remove materials from the container.
Traditionally, stoppers and similar closures were made of natural rubber. Over the years, various synthetic rubbers and other elastomers have been developed to improve the permeation resistance, sealability and other desirable properties of the closures. These include, for example, butyl rubbers, isoprene rubbers, fluorocarbon polymers, etc. These elastomers have high permeation resistance, are easily puncturable by a syringe needle, and are sufficiently elastic to allow easy insertion into a container opening and to provide a good seal with the edge or wall of the opening. The containers are typically made of glass or plastic.
Many biological materials, pharmaceuticals and other cryophilic materials must be stored in sealed containers maintained at temperatures below about −80° C., for example to avoid deterioration or evaporation loss of these materials. The materials include, for example, blood, serum, proteins, peptides, stem cells, DNA, and other perishable biological liquids, on the one hand, and freeze-dried or lyophilized products, on the other hand. These materials are typically stored in stoppered glass vials or other glass or plastic containers with an elastomeric closure.
A problem with elastomeric closures for cryogenic applications is that currently available elastomeric closures undergo a glass transition between about −50° C. and −65° C. Once glass transition occurs, the elastomeric closure becomes hard, and even brittle, like glass, and the integrity of the seal between the closure and the container is compromised. This allows vapors, gases and possibly liquids to pass between the closure and the container opening, resulting in contamination of the contained sample and/or partial loss of the sample by evaporation or sublimation. While elastomeric materials are known which have a glass transition temperature (Tg) below about −80° C., such elastomeric materials are often expensive and/or may have undesirable properties, such as insufficient permeation resistance or tendencies to contaminate the contained product by chemicals present in the elastomer.
Accordingly, it would be desirable to have an elastomeric stopper or closure for vials and other containers, which are subjected to cryogenic temperatures for processing, storage and the like, such that the stopper or closure will maintain sufficient elastomeric properties to effect a complete seal of the container opening at temperatures below about −80° C., while retaining the desirable properties of permeation resistance, puncturability, and other functional or compatibility properties of current closures.